---
layout: docs
page_title: Nomad Container Storage Interface (CSI) volume specification
description: |-
  Learn about the Nomad Container Storage Interface (CSI) volume
  specification. Define capacity, capabilities, mount
  options, secrets, topology requests, and a context map of values passed
  directly to the CSI plugin to validate the volume. Learn how volume
  creation and registration are different. Additionally, learn how to
  expand the size of a volume and update a volume definition.
---

# Nomad Container Storage Interface (CSI) volume specification

This page provides reference information for the Nomad Container Storage
Interface (CSI) volume specification. Create and register CSI volumes using the
[`volume create`][] and [`volume register`][] commands and the [`PUT
/v1/volume/csi/:volume_id/create`][api_volume_create] and [`PUT
/v1/volume/csi/:volume_id`][api_volume_register] API endpoints. Define capacity,
capabilities, mount options, secrets, topology requests, and a context map of
values passed directly to the CSI plugin to validate the volume.  Learn how
volume creation and registration are different. Additionally, learn how to
expand the size of a volume and update a volume definition.

Some attributes are only supported by a specific operation, while others may
have a different meaning for each action, so read the documentation for each
attribute carefully. The section [Differences Between Create and
Register](#differences-between-create-and-register) provides a summary of the
differences.

Provide the file as either HCL or JSON to the commands and as JSON to the API.

## Parameters

- `capability` <code>([Capability][capability]: &lt;required&gt;)</code> -
  Option for validating the capability of a volume.

- `capacity_min` `(string: <optional>)` - Option for requesting a minimum
  capacity, in bytes. The capacity of a volume may be the physical size of a
  disk, or a quota, depending on the storage provider. The specific size of the
  resulting volume is somewhere between `capacity_min` and `capacity_max`; the
  exact behavior is up to the storage provider. If you want to specify an exact
  size, you should set `capacity_min` and `capacity_max` to the same
  value. Accepts human-friendly suffixes such as `"100GiB"`. This field may not
  be supported by all storage providers. Increasing this value and reissuing
  `volume create` or `volume register` may expand the volume, if the CSI plugin
  supports it.

- `capacity_max` `(string: <optional>)` - Option for requesting a maximum
  capacity, in bytes. The capacity of a volume may be the physical size of a
  disk, or a quota, depending on the storage provider. The specific size of the
  resulting volume is somewhere between `capacity_min` and `capacity_max`; the
  exact behavior is up to the storage provider. If you want to specify an exact
  size, you should set `capacity_min` and `capacity_max` to the same
  value. Accepts human-friendly suffixes such as `"100GiB"`. This field may not
  be supported by all storage providers.

- `clone_id` `(string: <optional>)` - If the storage provider supports cloning,
  the external ID of the volume to clone when creating this volume. If omitted,
  the volume is created from scratch. The `clone_id` cannot be set if the
  `snapshot_id` field is set. Only allowed on volume creation.

- `context` <code>(map<string|string>:nil)</code> - An optional key-value map of
  strings passed directly to the CSI plugin to validate the volume. The details
  of these parameters are specific to each storage provider, so consult the
  specific plugin documentation for more information. Only allowed on volume
  registration. Note that, like the rest of the volume specification, this block
  is declarative, and an update replaces it in its entirety, therefore all
  parameters need to be specified.

- `external_id` `(string: <required>)` - The ID of the physical volume from the
  storage provider. For example, the volume ID of an AWS EBS volume or Digital
  Ocean volume. Only allowed on volume registration.

- `id` `(string: <required>)` - The unique ID of the volume. This is how the
  [`volume.source`][csi_volume_source] field in a job specification refers to
  the volume.

- `mount_options` <code>([MountOptions][mount_options]:
  &lt;required&gt;)</code> - Options for mounting `file-system` volumes that
  don't already have a pre-formatted file system.

- `name` `(string: <required>)` - The name of the volume. On volume creation,
  the external storage provider may use this field to tag the volume or as an
  idempotency token, so it must be unique across all namespaces.

- `namespace` `(string: <optional>)` - The namespace of the volume. This field
  overrides the namespace provided by the `-namespace` flag or `NOMAD_NAMESPACE`
  environment variable. Defaults to `"default"` if unset.

- `parameters` <code>(map<string|string>:nil)</code> - An optional key-value map
  of strings passed directly to the CSI plugin to configure the volume. The
  details of these parameters are specific to each storage provider, so consult
  the specific plugin documentation for more information.

- `plugin_id` `(string: <required>)` - The ID of the [CSI plugin][csi_plugin]
  that manages this volume.

- `secrets` <code>(map<string|string>:nil)</code> - An optional key-value map of
  strings used as credentials for publishing and unpublishing volumes.

- `snapshot_id` `(string: <optional>)` - If the storage provider supports
  snapshots, the external ID of the snapshot to restore when creating this
  volume. If omitted, the volume is created from scratch. The `snapshot_id`
  cannot be set if the `clone_id` field is set. Only allowed on volume creation.

- `topology_request` <code>([TopologyRequest][topology_request]: nil)</code> -
  Specify locations such as region, zone, and rack where the provisioned volume
  must be accessible from in the case of volume creation, or the locations where
  the existing volume is accessible from in the case of volume registration.

- `type` `(string: <required>)` - The type of volume. Must be `"csi"` for CSI
  volumes.

## Differences between create and register

Several fields are set automatically by the plugin when `volume create` or
`volume register` commands are successful and you should not set their values if
they are not supported by the operation.

On **volume registration** you should not set the [`snapshot_id`](#snapshot_id),
or [`clone_id`](#clone_id) fields.

On **volume creation** you should not set the [`external_id`](#external_id) or
[`context`](#context) fields.

## Update a volume definition

The `volume register` command allows updating a volume definition. However,
after volume registration, you are only allowed to update the following fields:

* `capacity_min` and `capacity_max`. You may increase the volume size if the CSI
  plugin supports it. Expansion may or may not be possible while the volume is
  in use, again depending on the plugin.  Reducing volume capacity is not
  allowed per the CSI spec.
* `mount_options` block if the volume is not in use.
* `secrets` block
* `context` block. The values for this field are typically provided by the CSI
  plugin and should not be updated unless recommended by the CSI plugin's
  documentation.

Additionally, you may add or remove `capability` blocks, but only if the
capability is not currently in use by a mounted volume.

## Volume expansion

You may expand CSI Volumes if the CSI controller plugin and node plugin, if
required, has the `EXPAND_VOLUME` capability.

To trigger a volume expansion, increase [`capacity_min`](#capacity_min) above
the current real capacity of the volume, as received from the [`volume
status`][] command, and re-issue either [`volume create`][] or [`volume
register`][].

Nomad reconciles the requested capacity by issuing expand volume requests to the
controller plugin, and if required by the controller, also to the node plugins
for each allocation that has a claim on the volume.

## Examples

### Volume registration

This is an example file used for the [`volume register`][] command.

```hcl
id              = "ebs_prod_db1"
name            = "database"
type            = "csi"
external_id     = "vol-23452345"
plugin_id       = "ebs-prod"

capability {
  access_mode     = "single-node-reader-only"
  attachment_mode = "file-system"
}

capability {
  access_mode     = "single-node-writer"
  attachment_mode = "file-system"
}

mount_options {
  fs_type     = "ext4"
  mount_flags = ["noatime"]
}

topology_request {
  required {
    topology { segments { "rack" = "R2" } }
    topology { segments { "rack" = "R1", "zone" = "us-east-1a"} }
  }
}

secrets {
  example_secret = "xyzzy"
}

parameters {
  skuname = "Premium_LRS"
}

context {
  endpoint = "http://192.168.1.101:9425"
}
```


### Volume expansion

Either [`volume create`][] or [`volume register`][] commands can trigger
an expand to occur, after the volume has already been created or registered.

This example shows you how to expand a volume using the `volume create` command.

1. Create a volume configuration file called `volume.hcl` that defines ID, name,
   type, plugin ID, and capacity.

   ```hcl
   id        = "ebs_prod_db1"
   name      = "database"
   type      = "csi"
   plugin_id = "ebs-prod"

   capacity_min = "50gib"
   capacity_max = "50gib"

   # ... etc ...
   ```

1. Create the volume using the [`volume create`] command.

   ```shell-session
   $ nomad volume create volume.hcl
   Created external volume vol-asdf1234 with ID ebs_prod_db1
   ```

1.  Review the volume's current capacity using the [`volume status`] command.

   ```shell-session
   $ nomad volume status ebs_prod_db1 | grep Capacity
   Capacity             = 50 GiB
   ```

1. Increase volume capacity in the `volume.hcl` file.

   Update the `capacity_min` and `capacity_max` fields.

   ```hcl
   id        = "ebs_prod_db1"
   name      = "database"
   type      = "csi"
   plugin_id = "ebs-prod"
   # all of the above must remain the same

   capacity_min = "100gib" # double
   capacity_max = "100gib" # increased to match

   # ... etc ...
   ```

1. Expand the volume using the [`volume create`] command.

   ```shell-session
   $ nomad volume create volume.hcl
   Created external volume vol-asdf1234 with ID ebs_prod_db1
   ```

1. Review the new capacity by running the [`volume status`] command.

   ```shell-session
   $ nomad volume status ebs_prod_db1 | grep Capacity
   Capacity             = 100 GiB
   ```

If you encounter errors that are not clear from the command output,
the CSI plugin allocation logs and Nomad leader server logs may be
helpful.

[api_volume_create]: /nomad/api-docs/volumes#create-csi-volume
[api_volume_register]: /nomad/api-docs/volumes#register-csi-volume
[capability]: /nomad/docs/other-specifications/volume/capability
[csi_plugin]: /nomad/docs/job-specification/csi_plugin
[csi_volume_source]: /nomad/docs/job-specification/volume#source
[mount_options]: /nomad/docs/other-specifications/volume/mount_options
[topology_request]: /nomad/docs/other-specifications/volume/topology_request
[`volume create`]: /nomad/commands/volume/create
[`volume register`]: /nomad/commands/volume/register
[`volume status`]: /nomad/commands/volume/status
